Yes, it is. 'The True Confessions of Charlotte Doyle' is classified as historical fiction as it's set in a specific historical period and incorporates elements of that time.
Power struggle is a common theme. Captain Jaggery has a position of authority on the ship and Charlotte is a young girl trying to find her place. Their interactions often involve a push and pull of power. Another theme is the idea of redemption. In some fanfictions, Jaggery might be shown as having a chance to redeem himself in Charlotte's eyes. And of course, there's the theme of romance, exploring the possibility of a relationship between them despite their differences.
I'm not sure specifically which 'Charlotte Sweden love story' you mean. There could be many fictional or real - life love stories involving someone named Charlotte in Sweden. It could be a story of two people who met in a charming Swedish town, like Stockholm. Maybe Charlotte was a tourist and fell in love with a local there.
I don't know the specific Charlotte and Gaz love story. It could be a very personal and unique story that might involve them meeting by chance, perhaps at a coffee shop. They might have shared a common interest which sparked their initial connection.
In Secret Saturdays, Doyle's love story might be one of those slow - burn types. He could be initially attracted to someone who works in the same field of dealing with the unknown. Their relationship begins with mutual respect for each other's skills. Doyle might find himself constantly thinking about this person, and as they go on more and more missions together, he starts to see her in a different light. Eventually, they confess their feelings for each other during a particularly harrowing adventure, where they realize that life is too short not to be together.
There are likely some fanfiction communities on Tumblr as well that might have Captain Jaggery x Charlotte Doyle fanfiction. You can search relevant tags and see if any users have recommended or written stories about them. Tumblr is also a great place to interact with other fans who might be able to point you towards some great fanfiction pieces.